1. Field of the Invention
The present invention relates to a feedthrough of a submarine repeater and a submarine repeater and more particularly to a feedthrough of a submarine repeater and a submarine repeater having a waterproof structure for preventing infiltration of seawater.
2. Description of the Related Art
Conventionally, submarine repeaters of submarine cables using optical fibers are laid with submarine cables in the deep sea thousands of meters below the surface, so that the submarine repeaters receive a high seawater pressure. Accordingly, such submarine repeaters are required to have high pressure resistance and high water tightness.
Further, as disclosed in Patent Document 1, for example, a position where the submarine cable is introduced into the submarine repeater is provided with a feedthrough (structure for connecting an optical fiber to a repeater unit in the submarine repeater). Specifically, a pressure-resistant housing lid is disposed on both sides of a pressure-resistant housing for storing the repeater unit and the feedthrough is inserted into a through-hole formed on the pressure-resistant housing lid. In this case, the feedthrough is installed on the pressure-resistant housing lid with high pressure resistance and high water tightness so as not to allow infiltration of seawater into the pressure-resistant housing.
FIG. 1 shows a feedthrough 100 as a conventional example. FIG. 1 shows the feedthrough 100 installed on a pressure-resistant housing lid 110 in an enlarged manner. In the figure, to the right of the pressure-resistant housing lid 110 is seawater and to the left is an inside of the housing. A tail cable 103 is constructed by successively coating a copper pipe 125 and an insulator 126 onto a circumference of an optical fiber 123 in a laminated manner. The tail cable 103 is integrally connected to a tail cable introduction unit 122 constituting the feedthrough 100.
The cable introduction unit 122 has a cap member 131 installed on a circumferential portion thereof. The cap member 131 includes first and second members 132 and 133 made of metal.
The first member 132 is fixed on the insulator 126 positioned at an outermost circumference of the cable introduction unit 122 in an inner side of the housing relative to the cable introduction unit 122 (left side of the figure). Further, the second member 133 is fixed on the cable introduction unit 122 by being screwed up on the first member 132. Moreover, the cable introduction unit 122 on which the cap member 131 is installed is fixed on the pressure-resistant housing lid 110 using a nut 134.
A boundary surface 143 where the first and second members 132 and 133 are brought into contact through screwing is a surface also in contact with the insulator 126 made of resin. In this manner, the boundary surface 143 is an extremely important portion in which the first and second members 132 and 133 made of metal and the insulator 126 are brought into contact and seawater pressure is applied, so that voltage resistance, water pressure resistance, and airtightness are required in particular at the same time. Thus, high reliability is required.
In view of this, conventionally, a rubber cap 141 is disposed between the cap member 131 and the tail cable 103 and polybutene 140 (insulating oil) is filled in a clearance formed by the rubber cap 141, cap member 131, and the tail cable introduction unit 122. Accordingly, a polybutene injection portion 142 for filling the polybutene 140 is disposed on the second member 133 and the polybutene injection portion 142 is closed using a screw after the polybutene 140 is filled.
In this structure, compression of the polybutene 140 from seawater pressure and volume change from heat are absorbed through elastic deformation of the rubber cap 141. Further, the rubber cap 141 and the tail cable 103 are strapped with a tape 165 such that seawater is not filtrated between the rubber cap 141 and the tail cable 103.
Patent Document 1: Japanese Laid-Open Patent Application No. 2002-118948
However, in the conventional feedthrough 100, the rubber cap 141 must be disposed between the second member 133 and the tail cable 103 in a liquid-tight manner so as to absorb the compression of the polybutene 140 from seawater pressure and the volume change from heat. Further, the cap member 131 requires the polybutene injection portion 142 for filling the polybutene 140 and the screw for closing the polybutene injection portion 142 with a high airtightness. Thus, the structure of the feedthrough 100 is complicated, so that a number of components is increased and assembly is troublesome.
Further, upon filling the polybutene 140, it is necessary to perform the filling without allowing air bubbles to get into the polybutene 140. Thus, in a conventional process, the portion to fulfill the polybutene 140 is subjected to vacuuming via the polybutene injection portion 142, and then the polybutene 140 is injected. Accordingly, the process for filling the polybutene 140 is very troublesome.
Moreover, when the submarine repeater on which the feedthrough 100 is installed is subjected to an airtightness test of the pressure-resistant housing, helium gas is supplied to the inside of the pressure-resistant housing. In the airtightness test, the feedthrough 100 is in contact with the helium gas, so that helium gas with small molecules may get into the insulator 126 (polyethylene and the like) made of resin. This is problematic in that the helium may be permeated from the insulator 126 after the test and the polybutene 140 may leak out resulting from this.